This time they stood in front of a D.C. bridge that will cost $661 million to replace, but the whole point was that they could have used about 10,000 different places in America as their backdrop for an example of something critical that’s falling apart.

The report card by the American Society of Civil Engineers showed the national infrastructure a single grade above failure, a step from declining to the point where everyday things simply stop working the way people expect them to.

“When we’re talking about infrastructure, we never compute the cost of inaction,” said former Pennsylvania governor Edward G. Rendell, who now heads a coalition that promotes investment in infrastructure. “The cost of inaction is greater than the cost of doing something. It’s become this literally crazed idea that spending money is bad. Federal governments and state governments have to spend money on certain things that are important.”

Using ratings by civil engineers in every state, the ASCE gave the national infrastructure an overall grade of D-plus, an average pulled down by some of the biggest problem areas — aviation, drinking-water supply, roads, transit and sewage treatment.

Restoring it all to good working order will require an investment of $3.6 trillion by 2020, the ASCE concluded, and if the current level of spending continues it will fall short of that figure by $1.6 trillion. The call for vast new investment comes in an era of national austerity, and with a major source of infrastructure funding on the brink of bankruptcy.

“These systems are the foundation. We need a commitment to bring infrastructure into a state of good repair,” said ASCE President Gregory E. DiLoreto, standing by the Anacostia River with the dilapidated Frederick Douglass Memorial Bridge looming behind him. “We need leadership at all levels of government.”

Maryland received a rating of C-minus from its civil engineers, scoring best for its restoration of bridges but low for managing storm water that flows into the Chesapeake Bay. Virginia scored a D-plus, with its better grades for parks, aviation and waterways, while it narrowly missed a failing grade for its handling of more than 1,000 dams. While the District did not receive an overall grade, the report noted that 99 percent of its streets were judged in poor or mediocre condition.

The experts, joined by an outspoken cadre of former secretaries of transportation and by those who run different parts of the country’s infrastructure, have been sounding the warning for several years now. Their reports and studies all reach the same dire conclusion, but so long as lights come with a flick of the switch, streets are fairly smooth, water flows from the faucet, and trains and planes run mostly on time, their message does not seem to connect with most average Americans.

In rating 16 areas of infrastructure, the engineers did find a couple of things to be happy about. With 34 percent of the nation’s trash now being recycled, solid waste management received a grade of B-minus.

A $75 billion capital investment in railroads since 2009 has resulted in “a competitive resurgence as both an energy-efficient freight option and a viable city-to-city passenger service,” the ASCE said. Freight rail companies renewed 3,100 miles of track in 2010, the report said.

The study awarded those rail efforts with a C-plus, which helped elevate the grade for all 16 categories to a D-plus, bumping it up from last year’s flat D.

The news was not so good on aviation, where the engineers said the ability of the nation’s system to handle demand was so stretched that airport congestion and delays cost $22 billion in 2012.

Aviation got a D, as did the nation’s transit systems. The ASCE said investment in deteriorating transit systems has not kept pace with a more than 9 percent ridership increase in the past decade, a demand that the group projects will continue to grow.

School construction, rarely broken out in a separate category in infrastructure reports, has declined to about half of what it was before the recession, the report said. While there is little data on the state of the nation’s school buildings, the report pointed out that most of them were built to serve baby boomers, who now are at or near retirement age.

Roadways, which generally get the most attention in these studies, again rated a D. The report noted that 42 percent of major urban highways are congested and that drivers and transport companies spend an estimated $101 billion a year in time and fuel while sitting in traffic.

The study’s worst grades — a pair of D-minuses — were to two critical areas that escape public notice except when they fail. Inland waterways, called “the hidden backbone of our freight network,” have not been updated since the 1950s, and their current state of disrepair causes delays that cost consumers.

The ASCE has been at the forefront of groups warning that post-World War II infrastructure is at the end of its natural life-span and needs immediate attention. But it has been joined by virtually every other national group with a stake in the game.

The American Association of State Highway and Transportation Officials has estimated a need for $13 billion in investment in bridges in the next 50 years.

One of the best bottom-line cost estimates came from an expert panel convened two years ago by the Miller Center of Public Affairs at the University of Virginia. To maintain infrastructure at current levels, $134 billion to $194 billion more needs to be spent each year through 2035. The federal government alone should come up with $2.3 trillion over that period.

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